The invention relates to using mechanical connection to assemble together parts made of thermostructural composite material, such as a ceramic matrix composite (CMC) material or a carbon-carbon (C/C) material, which material is typically made up of a porous substrate such as a porous fiber substrate, that is densified with a matrix. The fibers of the substrate may in particular be carbon fibers or ceramic fibers. The matrix is a refractory ceramic, such as for example: a carbide, an oxide, a nitride, a boride, or a refractory oxide. Thermostructural composite materials are remarkable for their mechanical properties, which make them suitable for constituting structural elements, and for their ability to retain those properties at high temperatures.
The invention relates more particularly to the mechanical and thermal behavior of mechanical connections used for assembling together parts made of thermostructural composite material when those parts are to be immersed in high temperature streams, as applies for example when fabricating all or some of the afterbody assemblies of an aeroengine such as exhaust cones (also known as “plugs”) or flaps for variable-section nozzles, or indeed any other hot fairing such as the aft fairing on a pylon for attaching an engine to an aircraft, known as the aft pylon fairing (APR).
In such applications, the parts that are to be assembled together are generally relatively fine (thickness of a few millimeters) and they need to satisfy aerodynamic requirements, which makes it preferable to use fastener elements of the plane surface or “flush” type in order to make mechanical connections between the parts. For assemblies that are used to make afterbody portions of an aeroengine, it is general practice to use fastener elements that present a flat head at one end of the fastening, which head is received in a countersink formed in one of the parts to be assembled together, and a spacer or a washer at the other end for enabling differential expansion to be taken up between the fastener elements, which expand significantly, and the parts made of thermostructural composite material, which expand less. Incorporating the head of the fastener element flush in a countersink present at one end of the fastening serves to obtain good aerodynamic performance. Nevertheless, the pre-loading or tightening force that is applied to the connection by the fastener element needs to be limited in order to ensure that the parts for assembling together and that are made out of composite material are not damaged by crushing and/or shear.